Many problems of conductivity and reliability are posed in circuit patterns which are more dense and more closely packed together. For example, low resolution screen printing and etching methods provide edge smears which tend to short together adajcent wires, thus limiting spacing between conductors to more than about 0.01 inch (0.025 cm). Also, the conventional methods of plating or depositing printed wires, which usually are thinner than 0.001 inch (0.003 cm), results in very low conductivity wiring when the conductor widths are less than about 0.006 inch (0.015 cm).
Even more restrictive in practical low cost systems is the nature of the substrates. Conventional substrates have significant surface irregularities from their fibrous construction, and thus the surface irregularities significantly increase the chance for defects in high density printed wiring patterns directly placed thereupon.
Attempts have been made to photographically reproduce high resolution printed wiring patterns as shown by U.S. Pat. No. 2,585,700 to S. W. Strickman of Feb. 12, 1952, wherein photographically processed gelatin layer patterns are processed as a mold to receive conductors which are threafter, when the gelatin is removed, cast into a resin which serves as a substrate. Not only is this a tedious and costly process but the conductors are very thin and thus very low in conductivity.
A general object of this invention therefore is to correct the general deficiencies of the prior art.
It is therefore a more specific objective of this invention to produce printed circuits in an inexpensive process using performed printed wiring board substrates of a conventional nature to obtain reliable and precise circuits which may be densely packed and yet have high conductivity.